Electrical connector

ABSTRACT

An electrical terminal (1) for connection to one or more electrical wires comprises a conventional terminal portion (2) having a lug portion (3) and a hollow shank (4), a jacket (11) of polymeric insulation that extends over the shank, and a tapering hollow connection piece (6) for example in the form of a coiled wire. The tapering connection piece has an internal and external screw thread and is arranged partly within the end of the shank. It is capable of receiving one or more electrical wires so that they can be secured within the connection piece (6), and the connection piece (6) can be secured within the shank (5) by twisting the terminal about the wires. The jacket (11) is preferably formed from a heat-shrinkable sleeve, and the terminal preferably includes a quantity of solder (9) for forming a permanent electrical connection.

This invention relates to electrical connectors and especially toelectrical terminals for forming a connection between one or moreelectrical wires and a further, fixed, electrical terminal for example ascrew terminal.

A number of terminals for wires have been proposed in which a shank ofthe terminal is crimped about the end of a wire after stripping the wireof insulation. One such terminal, for example, is described in ourinternational patent application No. WO90/00819. In addition, it hasbeen proposed to manufacture terminals in which the shank is connectedto the wire by means of solder for example using a solder ring locatedwithin a dimensionally heat-recoverable sleeve.

These terminals suffer from the disadvantage that they have relativelylittle tolerance to the size of wire to be terminated, with the resultthat one must employ a large number (usually at least four) differentsizes of terminals for each range of wires or cables to be terminated,especially in the case of crimp terminals. While terminals employing asolder connection are usually quite satisfactory as concerns electricalcontinuity they often do not exhibit sufficient resistance to tensilestrain. Furthermore, such terminals are often not easily employable withsolid conductor wires.

According to the present invention, there is provided an electricalterminal for connection to one or more electrical wires, which comprisesa terminal portion having a lug portion and a hollow shank, a jacket ofpolymeric insulation that extends over the shank, and a tapering hollowconnection piece that has an internal and an external screw thread, theconnection piece being arranged partly within the end of the shank andbeing capable of receiving one or more electrical wires so that the wireor wires can be secured within the connection piece and the connectionpiece can be secured within the shank by twisting the terminal about thewire or wires.

Thus, by means of the present invention it is possible to terminate oneor more than one wires at a single terminal where the wire gauges varysignificantly, and produce a termination with relatively low electricalresistance and high tensile strength.

The connecting element may, if desired, by formed from a solid block ofmetal that has been tapped both internally and externally with a screwthread. However it is preferred, both in terms of ease of manufactureand effectiveness in use, to employ a metal wire that has been woundinto a tapering helix, preferably a frusto-conical helix. Such a form ofconnection piece has the advantage that it will be locked in position inthe end of the terminal shank as the wire or wires are screwed into itin a similar manner to a nut mounted within a bolt. The wire may beformed with a circular cross-section, although it is preferred for thewire to have a relatively sharp ridge along its length, eg. formed bycold drawing or cold rolling, which, when the wire has been coiled, isdirected toward the interior of the coil in order to form the screwthread. In particular it is advantageous for the wire to be formed witha polygonal, and especially a square or diamond-shaped, cross-section.The wire may be formed from any appropriate metal or metal alloy, butpreferably is formed from copper, and especially from copper havingsubstantially the same purity as that conventionally employed forelectrical conductors.

The insulating jacket is preferably at least partially dimensionallyrecoverable and especially dimensionally heat-recoverable, that is tosay, it has a dimensional configuration that may be made to change whensubjected to heat treatment.

Usually these articles recover, on heating, towards an original shapefrom which they have previously been deformed but the term"heat-recoverable", as used herein, also includes an article which, onheating, adopts a new configuration, even if it has not been previouslydeformed.

In their most common form, such articles comprise a heat-shrinkablesleeve made from a polymeric material exhibiting the property of elasticor plastic memory as described, for example, in U.S. Pat. Nos.2,027,962; 3,086,242 and 3,597,372. As is made clear in, for example,U.S. Pat. No. 2,027,962, the original dimensionally heat-stable form maybe a transient form in a continuous process in which, for example, anextruded tube is expanded, whilst hot, to a dimensionally heat-unstableform but, in other applications, a preformed dimensionally heat-stablearticle is deformed to a dimensionally heat-unstable form in a separatestate.

In the production of heat-recoverable articles, the polymeric materialmay be cross-linked at any stage in the production of the article thatwill enhance the desired dimensional recoverability. One manner ofproducing a heat-recoverable article comprises shaping the polymericmaterial into the desired heat-stable form, subsequently cross-linkingthe polymeric material, heating the article to a temperature above thecrystalline melting point or, for amorphous materials the softeningpoint, as the case may be, of the polymer, deforming the article andcooling the article whilst in the deformed state so that the deformedstate of the article is retained. In use, since the deformed state ofthe article is heat-unstable, application of heat will cause the articleto assume its original heat-stable shape.

Any material to which the property of dimensional recoverability may beimparted may be used to form the sleeve. Preferred materials includelow, medium or high density polyethylene, ethylene copolymers, eg. withalpha olefins such as 1-butene or 1-hexene, or vinyl acetate, polyamidesor fluorpolymers, eg. polytetrafiuoroethylene, vinylidine fluoride orethylenetetrafluoroethylene copolymer.

The jacket preferably extends not only over the shank of the terminationbut also beyond the end of the shank into which the wire or wires willbe introduced so that it encloses the connection piece and the proximalend regions of the wire or wires thus providing electrical insulationfor the metallic elements in the termination and aiding the resistanceto moisture ingress.

The terminal is preferably provided with a quantity of sealant toprevent to reduce ingress of moisture into the shank from the region ofthe lug portion. Normally, the sealant will be provided as a gel or afusible plastics insert. The term "gel" as used herein is intended tomean a liquid-extended polymer composition. Such compositions normallycontain a three-dimensional network of cross-linked molecular chains andpreferably include at least 300 parts, more preferably at least 500parts by weight of extender liquid per 100 parts by weight of thepolymer composition. The gel used in the invention preferably has a conepenetration value (measured by ASTM D217) within the range of from 100to 400 10⁻¹ millimeters, more preferably 100 to 350 10⁻¹ millimeters; anultimate elongation (measured by ASTM D412) preferably greater than100%, with substantially elastic deformation to an elongation ofpreferably at least 100%; and ultimate tensile strength (ASTM D412)preferably less than 1 MegaPascal.

The polymer composition may for example comprise an elastomer, or ablock copolymer having relatively hard blocks and relatively elastomericblocks. Examples of such copolymers include styrene-diene blockcopolymers, for example styrene-butadiene or styrene-isoprene diblock ortriblock copolymers, or styrene-ethylene-butylene-styrene triblockcopolymers as disclosed in international patent publication numberWO88/00603. The extender liquids employed in the gel preferably compriseoils conventionally used to extend elastomeric materials. The oils maybe hydrocarbon oils, for example paraffinic or naphthenic oils,synthetic oils for example polybutene or polypropene oils, and mixturesthereof. The preferred oils are mixtures of non-aromatic paraffins andnaphthenic hydrocarbon oils. Suitable gels can also be prepared bycuring reactive silicones with non-reactive extender silicones. The gelmay contain known additives such as moisture scavengers (eg. benzoylchloride), antioxidants, pigments and fungicides.

Where the sealant is provided in the form of a fusible plastics insertit may be located in an end portion of the jacket that is positionedover the end of the shank, or it may be located within the shank itselfso that it will melt and block the shank when the terminal is heated.

The fusible plastics insert is preferably one formed from an olefinhomo- or copolymer with other olefins, or ethylenically unsaturatedmonomers, eg. high, medium or low density polyethylene and ethylenecopolymers with alpha olefins especially C₃ to C₈ alpha olefins, vinylacetate or ethyl acrylate; polyamides, polyesters, halogenated polymersand the like. Preferred polyamides include those polyamides having anaverage at least 15 carbon atoms between amide linkages for examplethose based on dimer acids and/or dimer diamines. Examples of suchadhesives are given in U.S. Pat. Nos. 4,018,733 to Lopez et al and4,181,775 to Corke et al. Preferred polyesters include polybutyleneterephthalate and butylene ether butylene terephthalate blockcopolymers.

The insulating jacket will normally extend beyond the end of the shankremote from the lug portion and will contain a further quantity ofsealant to prevent or reduce ingress of moisture into that end of theshank. The sealant may comprise a gel or an insert of fusible plasticsmaterial as described above, and a combination of both forms of sealantmy be employed at different ends of the insulating jacket.

Where a gel is used as a sealant it is appropriate to employ some meansof keeping it in compression during service. Thus, for example, theinsulating jacket may include a metal ring that can be crimped about anywires that are inserted in the termination in order to maintain the gelunder compression and to assist in strain relieving the wire or wireswhen bent.

If desired a permanent solder connection may be formed by including aquantity of solder in the termination. The solder may, for example,simply be in the form of an Sn₆₃ Pb₃₇ eutectic composition which willmelt as the device is heated and the sleeve recovers, or more than onesolder composition having differing melting points may be employed, asdescribed in International Application No. WO88/09068. In this form ofdevice, melting of the higher melting point component, eg. Sn₉₆.5 Ag₃.5eutectic will provide a visual indication that the device has beenheated sufficiently to melt the lower melting point composition and toform a satisfactory solder joint. If desired the lower melting pointsolder may be a non-eutectic composition and, for example as describedin International Application No. PCT/GB90/00234, the higher and lowermelting point solder compositions may together form a eutecticcomposition. For example, a non-eutectic Sn₆₀ Pb₄₀ lower melting pointcomponent may be employed with a higher melting point component formedfrom pure tin in relative amounts that an Sn₆₃ Pb₃₇ eutectic is formed.The disclosures of these two patent applications are incorporated hereinby reference. An advantage of employing a two component solder, andespecially a tin, Sn₆₀ Pb₄₀ combination is that it reduces thepossibility of "wicking" that is to say, travel of the solder along theconductors and away from the joint area due to capillary action by thestranded conductors, which can be caused by prolonged heating of thedevice.

The solder may be positioned anywhere where it will be able to flow intothe connecting .element to fore a solder joint. The solder may beemployed in the fore of a ring or in any other fore for example a ball,and may be disposed symmetrically about the sleeve axis or offset fromit. The solder element may, for instance, be located at the smallerdiameter end of the connecting element in which case it may be in theform of a ball or plug, or it my be located in the region of a largediameter end of the connecting element, for example in the form of aring. Preferably the solder is in the from of an element that surroundsthe connecting element, especially where the connecting element is inthe fore of a coil so that the fused solder can flow through thewindings of the coil to the interior thereof. In the case of connectingelements formed from solid blocks of metal, it is advantageous toprovide the connecting element with one or more holes around itsperiphery to allow fused solder to flow into the interior of theconnecting element.

The particular form of the lug portion does not fore part of theinvention and any conventional fore of lug may be employed.

Two forms of termination will now be described by way of example withreference to the accompanying drawings, in which:

FIG. 1 is an isometric view of a terminal and connecting piece employedin the present invention;

FIG. 2 is a side view, partly in section, of a terminal according to theinvention;

FIG. 3 is a cross-section through the wire employed to form theconnecting piece; and

FIG. 4 is a side view, partly in section, of a second form of terminalaccording to the invention.

Referring to the accompanying drawings a terminal 1 comprises aconventional pressed copper or aluminium terminal portion 2 whichcomprises a lug 3 and a hollow open-ended shank 4 extending therefrom. Asmall insert 5 of fusible plastics material, for example polyethylene,is provided at the end of the shank nearest the lug for sealing thefinal termination against moisture ingress. A connection piece 6 formedas a frusto-conical spring or coil of hard temper copper wire is locatedin the end of the shank 4 remote from the lug 3 so that its smallerdiameter end is enclosed within the shank while its larger diameter endis exposed. The copper wire has a diamond shaped cross-section as shownin FIG. 2 having two sharp ridges 7 and 8 and is coiled so that theridges form an internal and an external screw thread on the connectionpiece 6. Accordingly the connection piece 6 can be located in the end ofthe shank 4 simply by screwing it into the open end until it is tight.

A band 9 of pre-fluxed Sn₆₃ Pb₃₇ eutectic solder having a smaller band10 of Sn₉₆.5 Ag₃.5 high temperature solder is located over the exposedpart of the connection piece 6, and a heat-recoverable sleeve 11 oftransparent cross-linked polyvinylidine fluoride is partially recoveredover the shank 4 and connection piece 6. The sleeve 11 extends beyondthe end of the connection piece 6 for about half its length, andcontains a fusible annular insert 12 formed from polyethylene.

In operation several electrical wires whose ends have been stripped ofinsulation can be inserted into the open end of the heat-recoverablesleeve 11 and into the end of the connection element 6 as far aspossible. The terminal 1 is then twisted about the wires which has theeffect of tightening the grip of the connection piece 6 on the wires andalso of tightening the connection piece 6 within the shank 4 of theterminal. Finally the terminal is heated, for example by means of ahot-air gun or infrared lamp, by induction or by passing an electriccurrent through the terminal to cause Joule heating. This causes thesleeve 11 to recover about the wires and the solder bands 9 and 10 tomelts, flow between the windings of the connection element 6 and form asolder connection to the wires. At the same time the plastics inserts 5and 12 melt and form a seal against water ingress at both ends of thesleeve 11.

The terminal my be employed with wires having a wide range of conductorcross-section, for example from 0.5 to 7 mm² which may have solid orstranded conductors or in which some wires have solid conductors andsome stranded. Also the terminal may be fitted on a single wire.

A modification of the terminal is shown in FIG. 4. This terminalincludes a terminal portion 2 having a lug 3 and shank 4, a connectionpiece 6, heat-recoverable sleeve 11 and fusible plastics insert 5 asdescribed above with the exception that the sleeve 11 is formed fromcrosslinked nylon 11 or nylon 12 and has a thin adhesive lining. Also,the insert 5 has been fused before installation to seal the end of thesleeve 11 and the shank against water ingress. The terminal does notcontain any solder but instead has a copper crimp ring 20 which may becrimped about the wire insulation in order to provide strain reliefagainst bending of the wires. The sleeve 11 contains a quantity of a gel21 that fills the entire internal cross-sectional area of the sleeve.

In operation the wire or wires are inserted into the open end of thesleeve 11 until they abut the internal surface of the connection piece6, and the terminal is twisted about the wires as described above. Thecopper ring is then squeezed inwardly in order to put the gel 21 intocompression and to provide the wires with strain relief. No heating ofthe terminal is necessary for installation.

I claim:
 1. An electrical terminal for connection to one or moreelectrical wires, which comprises a terminal portion having a lugportion and a hollow shank, a jacket of polymeric insulation thatextends over the shank, and a tapering hollow connection piece that hasan internal and an external screw thread, the connection piece beingarranged partly within the end of the shank and being capable ofreceiving one or more electrical wires so that the wire or wires can besecured within the connection piece and the connection piece can besecured within the shank by twisting the terminal about the wire orwires.
 2. A terminal as claimed in claim 1, wherein the connection piececomprises a metal wire that is wound into a tapering helix, the woundwire forming the internal and external screw thread.
 3. A terminal asclaimed in claim 2, wherein the wire has a polygonal cross-section.
 4. Aterminal as claimed in claim 1 wherein the insulating jacket is at leastpartially dimensionally heat-recoverable.
 5. A terminal as claimed inclaim 1, which includes a quantity of sealant to prevent or reduceingress of moisture into the shank from the region of the lug portion.6. A terminal as claimed in claim 1, which includes a quantity ofpolymeric sealant located in an end region of the jacket of polymericinsulation that extends beyond the end of the shank to prevent or reduceingress of moisture into the end of the shank where the wire or wiresare inserted.
 7. A terminal as claimed in claim 1, wherein the polymericsealant is in the form of a gel.
 8. A terminal as claimed in claim 1,wherein the jacket includes a metal ring that can be crimped about anywires that are inserted.
 9. A terminal as claimed in claim 1, whereinthe polymeric sealant is in the form of an insert of a fusible plasticsmaterial.
 10. A terminal as claimed in claim 1, which includes aquantity of solder for forming a solder connection between the wires andthe connection piece.
 11. A terminal as claimed in claim 2, whichincludes a band of solder that extends around the connection piece andwill flow through the windings of the helix when heated.